In disk-type magnetic recording systems for digital applications, magnetic transducer elements, or heads, are used to write information onto (i.e., record) or read information from (i.e., playback) the disk surface or surfaces. Each head must be supported in close proximity to the associated disk surface, to permit low levels of magnetic flux to be employed and, in turn, high bit densities to be achieved.
To this end, each head is mounted in an aerodynamically designed member, termed a "slider"; together they comprise a slider/head (or head/slider) assembly. Rapid rotation of the disk causes a cushioning film of air to develop between the slider/head assembly and the disk surface; the slider flies over the disk surface, supported by this film. The air support is referred to as a bearing or, more specifically, the slider or air bearing.
An electro-mechanical positioning assembly, or actuator, is used to move each recording head to successive locations on the disk surface where information is to be either written or read. The positioner assembly includes one or more actuator arms and an actuuator motor. When multiple actuator arms are employed (e.g., in association with multiple disk surfaces), they move in unison. Each head is mounted near the end of an appropriate one of the actuator arms and the actuator motor moves the actuator arm(s) as one, to bring the head(s) into the desired position.
The magnetic heads and their sliders are not mounted directly on the actuator arms; rather, each head/slider assembly is mounted on a separate support structure which, in turn, is mounted to and suspended from an actuator arm.
Head positioning assemblies are generaly of two types: (1) linear and (2) rotary. Linear positioners move the actuator arms(s) and, thus, the head(s), along a linear path oriented parallel to a radius of the recording disk(s). Rotary positioners, by contrast, rotate the actuator arm(s) about a pivot point outside, but close to, the rim of the recording disk(s). This invention relates to rotary head positioners.
In the prior art, the magnetic head/slider assemblies and the supports used for suspending and sliding them over the disk surface(s) are cantilevered from an actuator arm which is substantially more massive by comparison. In general, the heads are employed and mounted in pairs, to reduce the access time required for positioning a head over a desired disk track; the two heads of each pair are cantilevered in parallel, spaced-apart relationship, both on one (i.e., the same) side of the actuator arm.
The design of a head support structure is dictated to a large extent by the requirement that read/write operation be unimpaired over the range of temperatures to be encountered in the disk drive. As temperature change, expansion and contraction of disk surfaces causes relative motion between disks and heads. To begin with, temperature variations affect the recording disks individually. Disk-to-disk termperature differentials give rise to other, further problems.
A typical recording disk comprises an aluminum or similar substrate which is coated with a ferro-magnetic material. The thermal properties of the disk are principally established by the thermal properties of the aluminum substrate. In general, each disk recording surface is divided into a number of concentric bands, or tracks, with adjacent tracks separated by a buffer zone. Information is recorded within the track boundaries. The position of each track and, correspondingly, the spacing between adjacent tracks, is a function of the temperature of the aluminum substrate; the disk substrate will expand or contract radially as the temperature varies.
Frequently, several (e.g., typically four or six) disks will be stacked on a common spindle. The actuator arms for these multiple disks are correspondingly stacked, in fixed relation to one another. One of the disk surfaces is used to record servo information which is used by the actuator motor control circuitry for locating the recording tracks on the other disk surfaces. If the temperature of the servo disk surface differs from that of the other disks, the servomechanism which drives the actuator arms may be unable to position the heads at the proper track locations. That is, temperature differentials may cause corresponding tracks to lose their vertical alignment.
Minimization of disk surface-to-disk surface temperature differences is necessary to resolve the latter problem. The former problem is dealt with by proper design of the head support structures.
To match the thermal coefficient of the aluminum disk substrate, the head/slider support assemblies are generally also made of aluminum. When each of a pair of heads is supported by such an aluminum structure, both are mounted to one side of the arm, in an attempt to make the spacing between the heads vary as a function of temperature in the same manner as the spacing between adjacent disk recording tracks varies.
Frequently, stainless steel is used as an additional element in a head support assembly, as a link between the aluminum head support elements and each head. The stainless steel member is fixed to the actuator arm and the aluminum head supports are, in turn, secured to the stainless steel member outboard of the arm.
Various disadvantages are attendant to such prior art structures. Chiefly, they are relatively massive, expensive to fabricate, and are not balanced.